This invention relates generally to towers. In particular, but not limited thereto, the present invention relates to wind turbine towers having an adapter between steel and concrete sections.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
Several technical installations require a tower or a mast to which the installation is mounted. Non-limiting examples of such installations are wind turbines, antenna towers used in broadcasting or mobile telecommunication, pylons used in bridge work, or power poles. Typically, the tower is made of steel and must be connected to a foundation made of reinforced concrete. In these cases, the typical technical solution is to provide a large, solid reinforced concrete foundation at the bottom of the tower. In typical applications the tower foundation extends about 12 meters below the ground level, and can be about 18 meters or more in diameter.
In larger utility grade wind turbines (e.g., 2.5 MW or more) it is often desired to have towers with heights of 80 meters or more. The higher hub heights provided by larger towers enable the wind turbine's rotor to exist in higher mean wind speed areas, and this results in increased energy production. Increases in tower height invariably have lead to corresponding increases in the mass, length and diameter of the tower. However, it becomes difficult to construct and transport large wind turbine towers as the local transportation infrastructure (e.g., roads, bridges, vehicles, etc.) often impose limits on the length, weight and diameter of tower components.